At the time when systematic science instruction starts, most children have already constructed a naïve theory of physics that makes it possible for them to interpret phenomena in the physical world. Theory is used here to denote a relational, explanatory structure, and not an explicit, wellformed, and sociallyshared scientific theory. This naïve theory is based on everyday experience and information coming from lay culture and is very different in its structure, in the phenomena it explains, and its individual concepts, from the scientific theories to which children are exposed in school. Learning science requires the fundamental restructuring of the naïve theory, a restructuring that can be referred to as theory change. More specifically, conceptual change can be defined as the outcome of a complex cognitive as well as social process whereby an initial framework theory is restructured. Studies of conceptual change have shown that this is a slow and gradual affair often accompanied by misconceptions, inert knowledge, internal inconsistencies, and lack of critical thinking.